This invention relates to a system for the detection of failures in the operation of automatic machine tools and, more particularly, to a system for the detection of a broken bit in boring machinery.
Many objects are fabricated today by the use of milling machinery for the shaping of various components of objects to be manufactured. Such milling machinery may be driven automatically by electronic control for mass production of components which are to be assembled to produce a desired end product. The milling machinery may have cutting heads of various shapes, which heads may be driven in different directions to accomplish a desired shaping of a component.
Of particular interest is the use of a boring machine in the manufacture of printed circuit boards for the electronics industry. The machine has a drill bit which is advanced towards a circuit board for cutting a through hole into the board. Frequently, many through holes are formed in a single circuit board, the drill head of the boring machine being automatically positioned relative to the circuit board during a succession of drilling operations. The drill head is precisely positioned at the various sites on the circuit board for precise location of the through holes, and provides for precise movement of the drill bit in a direction normal to the board for accurate formation of the through hole. A failure of the bit to form properly a desired through hole may necessitate rework of the circuit board, or a discarding of the circuit board.
A problem arises in that fatigue or other causes may induce fracture of the drill bit. Such fracture can occur during a drilling operation, and may go unnoticed until after a circuit board is examined for proper construction. The resulting lack of drilled holes can be costly to a manufacturing operation.
Solutions to the foregoing problem have been attempted by the design of broken drill bit detectors of various configurations. Unfortunately, none of these broken drill bit detectors have met with complete success due to inherent inaccuracies in the detection system, or due to circumstances such as excessive drilling dust blocking a sensor such as an optical sensor. Thus, there is a need for a more reliable apparatus for the detection of a failure in a cutting head, particularly the drill bit of a boring machine.